This invention relates to a method of operating a mobile telephone network, in particular a mobile ad hoc network, and to a mobile unit for use in such a method.
A mobile ad hoc network is usually superimposed on a conventional cellular network and involves data routes using nodes, usually provided by mobile units, as intermediate points, for example between a mobile unit and a base station.
In mobile ad hoc networks (MANETs), various communication devices with different features comprise a wireless network that has no fixed infrastructure and unpredictable connectivity. These nodes are not only the means to data interchange but also the managers for the routes to data and access to services. Many mobile devices in a MANET are likely to be battery operated, making energy exhaustion an important issue for network stability. As a consequence, energy consumption should be regarded as an essential metric in any MANET routing mechanism. See Cano, J.-C.; Dongkyun Kim, “Investigating performance of power-aware routing protocols for mobile ad hoc networks,” Mobility and Wireless Access Workshop 2002, MobiWac 2002. Many currently proposed power aware routing schemes are based on minimal total transmission power (MTTP), obvious examples being localized routing (LR) (Stojmenovic and X. Lin, “Power-aware Localized Routing in wireless Networks.” Parallel and Distributed Systems, IEEE Transactions on, Volume: 12 Issue: 11, November 2001), or residual battery energy (RBE), or conditional max-min battery capacity routing (CMMBCR) (C.-K. Toh, “Maximum Battery Life Routing to Support Ubiquitous Mobile Computing in Wireless Ad Hoc Networks,” IEEE Communications Magazine, June, 2001).
However, it is impractical to obtain an accurate value of the transmission power for MTTP, as this is dependant on the distance between nodes. In particular, the power needed to guarantee the transmission quality between two nodes can be estimated from k·dλ, where d is the distance between the nodes, k is the constant for estimation and λ is a value between 2 and 4. Because of the mobility of the nodes, d is difficult to obtain. GPS (the global positioning system) has been proposed to compute the distance, but this is an expensive option.
Moreover, the average end-to-end delay is increased due to the selection of routes with multiple hops.
When using RBE, more traffic load will be put on the node with the highest residual battery energy, which may result in rapid energy exhaustion. Consequently mechanisms based on such metrics cannot guarantee that the route can survive for the duration of an integrated service. For example, the service may comprise sending a 5 Mbit file from a source node to another node. The source node will invoke the route discovery procedure to find a proper route to send the file. If any node along the discovered route does not have enough energy to fulfil this service, then the transmission will be terminated and another route discovery procedure must be invoked, thus introducing inefficiency and wasting energy.
A low route survival probability (RSP) means the route is likely to become invalid during an integrated service, which will lead to unstable network connectivity and additional route discovery operations. This would require additional energy expenditure, especially under conditions of heavy traffic load.